Connector systems for interfacing diagnostic or analytical devices with an outside source of data are known. Generally, a connector system comprises at least two electrical interfaces, one on each of two sides of a connector module. On the first side of the connector module, the connector is interfaced with an outside source which generates a signal that is indicative of the state of a system under observation or otherwise activated. On the second side of the connector module, a second interface is provided to bus the signals from the outside source to an analytical or diagnostic device for analysis and data processing. Examples of such devices are ultrasound equipment, radar equipment, computer equipment, and other electronic devices which have an input interface. Connectors have been designed for use with all such devices and others.
In more sophisticated systems which implement high speed data links from the outside source to the device, the connector interfaces can become very complex. To achieve high integrity data communications between the outside source of data and the device, prior connectors have been designed to accommodate high density contacts so that increased data flow through the connector at high frequencies and at high speeds can be achieved. Examples of such connectors and connector systems are found in U.S. Pat. No. 4,699,593, Grabbe et al., and U.S. Pat. No. 4,927,369, Grabbe et al., the teachings of both being specifically incorporated herein by reference.
In the connectors such as those disclosed in the Grabbe et al. patents, the individual electrical interface contact members in the connector modules are usually on 100 mil centerlines which causes the size of the connector modules to increase dramatically as the contact count increases. Furthermore, the actuation forces necessary to achieve the interface between the second side of the connector and the device are greatly increased as the number of pins increases, thereby increasing the possibilities of misalignment of the connector and failure of the data interface. Additionally, many of these prior connectors are utilized in a manner requiring only a relatively small number of mating/unmating cycles.
Connectors to accommodate high contact densities for use in high speed data devices may comprise a plurality of modular connectors with electrical interface contacts as described above and a printed wiring board to which the modular connectors are plugged. The printed wiring boards also contain a plurality of circuits that are adapted to communicate the data from the outside source to the device which processes the data. The contact surfaces or pads on the printed wiring boards are typically interfaced with a substrate in the device which is further adapted to receive the communicated data from the outside source. This substrate may be yet another printed wiring board, printed circuit board, or other electrical receiving device which can interface with the contact pads on the printed wiring board in the connector.
When a high density of contacts is required, an interposer is also oftentimes provided to establish a connection medium between the printed wiring board and the substrate. An "interposer" is typically a land grid array which effectuates and/or facilitates contact between the printed wiring board and the substrate. Such interposers are especially useful when the closely spaced contact members on a connector prevent a direct interface to the printed wiring board. The interposer thus provides a separate set of contact elements which must be firmly secured against both the contact members of the connector and a printed wiring board in the device.
Connector modules for use with printed wiring boards in connector systems may be devised which utilize individual ones of the contact members or pins to provide a ground to the system. However, the use of individual pins physically limits the "signal-to-ground" ratio capabilities of the connectors. The "signal-to-ground" ratio is a parameter developed to quantify the efficiency of an electrical device, such as a printed wiring board, in an electrical system. In general, the lower the signal-to-ground ratio, the better the performance of the electrical component since the component will contain a larger number of ground interfaces with respect to the number of signal interfaces, thereby providing a clean signal to the system with good electrical integrity. The signal-to-ground ratio is determined by dividing the number of signal contacts in the component by the number of ground contacts or connections found in the component. For example, a coaxial cable which is terminated to a coaxial connector has a 1:1 signal-to-ground ratio since there is one ground conductor, usually an outer sheath, to one signal conductor, usually a center conductor wire. A similar problem has existed in card connectors or cable assemblies which have pins that are adapted to connect cables to computer boards. By placing a ground plane in between rows of pins in these connectors, the signal-to-ground ratio of the connector is desirably decreased.
Printed wiring boards in connector systems that utilize a plurality of such coaxial or microcoaxial cables, have a like plurality of signal contact pads associated with respective signal conductors, and conventionally a like plurality of ground contact pads which define a 1:1 signal-to-ground ratio for the board. In typical connector systems having a plurality of coaxial lines, the grounds of the individual coaxes are commoned and connected to a small number of pins for transmission through the connector module. This has the net effect of increasing the signal-to-ground ratio from the 1:1 of a coaxial cable to some higher number, typically 5:1 or larger.
This higher signal-to-ground ratio is a consequence of the desire in the art to minimize the pin count and associated assembly time required to put a modular connector together. Minimization of pin count is achieved since termination of the connector module generally involves gang soldering of the coax ground elements to a common circuit connected electrically to a single post in the connector module which ultimately connects to a ground contact of a mating connector in an electrical apparatus. By reducing the number of soldering operations to the post to a single common ground gang soldering operation, a great amount of manufacturing time is saved.
Thus a tension exists between (1) the need to miniaturize and modularize multicable connector modules tending to undesirably increase the signal-to-ground ratio, and (2) the desire to reduce the signal-to-ground ratio to maintain high electrical signal integrity for the connector. This tension is acutely felt in the design of high pin count and/or high density microcoaxial connectors for use as transmission media in high speed electronic applications. Particularly, microcoaxial interconnection schemes must maintain acceptable levels of signal integrity, particularly with respect to crosstalk, shielding, and controlled impedance. To maintain these high performance levels, the connectors must minimize effects of the impedance and shielding of the coaxial cables through the connector and across the separable interface. There has not been a solution heretofore in the art to address this tension.